rcu: Avoid resched_cpu() when rescheduling the current CPU

The resched_cpu() interface is quite handy, but it does acquire the
specified CPU's runqueue lock, which does not come for free.  This
commit therefore substitutes the following when directing resched_cpu()
at the current CPU:

	set_tsk_need_resched(current);
	set_preempt_need_resched();

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>